Magnetic tape and magnetic tape device

ABSTRACT

The magnetic tape includes a non-magnetic support; a non-magnetic layer including non-magnetic powder and a binder on the non-magnetic support; and a magnetic layer including ferromagnetic powder and a binder on the non-magnetic layer, in which the total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 μm, the magnetic layer includes a timing-based servo pattern, and logarithmic decrement acquired by a pendulum viscoelasticity test performed regarding the surface of the magnetic layer is equal to or smaller than 0.050.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2016-124933 filed on Jun. 23, 2016. The aboveapplication is hereby expressly incorporated by reference, in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape and a magnetic tapedevice.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes (hereinafter, also simplyreferred to as “tapes”) are mainly used for data storage such as databack-up or archive. The recording of information into magnetic tape isnormally performed by recording a magnetic signal on a data band of themagnetic tape. Accordingly, data tracks are formed in the data band.

An increase in recording capacity (high capacity) of the magnetic tapeis required in accordance with a great increase in information contentin recent years. As means for realizing high capacity, a technology ofdisposing the larger amount of data tracks in a width direction of themagnetic tape by narrowing the width of the data track to increaserecording density is used.

However, when the width of the data track is narrowed and the recordingand/or reproduction of magnetic signals is performed by allowing therunning of the magnetic tape in a magnetic tape device (normallyreferred to as a “drive”), it is difficult that a magnetic headcorrectly follows the data tracks in accordance with the position changeof the magnetic tape in the width direction, and errors may easily occurat the time of recording and/or reproduction. Thus, as means forpreventing occurrence of such errors, a system using a head trackingservo using a servo signal (hereinafter, referred to as a “servosystem”) has been recently proposed and practically used (for example,see U.S. Pat. No. 5,689,384A).

SUMMARY OF THE INVENTION

In a magnetic servo type servo system among the servo systems, a servopattern is formed in a magnetic layer of a magnetic tape, and this servopattern is magnetically read to perform head tracking. More specificdescription is as follows.

First, a servo head reads a servo pattern formed in a magnetic layer(that is, reproduces a servo signal). A position of a magnetic head ofthe magnetic tape in a width direction is controlled in accordance withvalues (will be described later specifically) obtained by reading theservo pattern. Accordingly, when running the magnetic tape in themagnetic tape device for recording and/or reproducing a magnetic signal(information), it is possible to increase an accuracy of the position ofthe magnetic head following the data track, even when the position ofthe magnetic tape is changed in the width direction with respect to themagnetic head. By doing so, it is possible to correctly recordinformation on the magnetic tape and/or correctly reproduce informationrecorded on the magnetic tape.

As the magnetic servo type servo system described above, a timing-basedservo type system is widely used in recent years. In a timing-basedservo type servo system (hereinafter, referred to as a “timing-basedservo system”), a plurality of servo patterns having two or moredifferent shapes are formed in a magnetic layer, and a position of aservo head is recognized by an interval of time when the servo head hasread the two servo patterns having different shapes and an interval oftime when the servo head has read two servo patterns having the sameshapes. The position of the magnetic head of the magnetic tape in thewidth direction is controlled based on the position of the servo headrecognized as described above.

Meanwhile, the magnetic tape is normally used to be accommodated andcirculated in a magnetic tape cartridge. In order to increase recordingcapacity for 1 reel of the magnetic tape cartridge, it is desired toincrease total length of the magnetic tape accommodated in 1 reel of themagnetic tape cartridge. In order to increase the recording capacity, itis necessary that the magnetic tape is thinned (hereinafter, referred toas “thinning”). As one method of thinning the magnetic tape, a method ofdecreasing the total thickness of a non-magnetic layer and a magneticlayer of a magnetic tape including the non-magnetic layer and themagnetic layer on a non-magnetic support in this order is used.

In consideration of these circumstances, the inventors have studied theapplication of a magnetic tape having a decreased total thickness of anon-magnetic layer and a magnetic layer to a timing-based servo system.However, in such studies, it was clear that, a phenomenon which was notknown in the related art occurred, in which an output of a servo signalreproduced by a servo head is decreased compared to that in an initialrunning stage (hereinafter, also referred to as an “output decrease of aservo signal”) occurs, when a head tracking is continuously performedwhile causing the magnetic tape to run in a timing-based servo system,in a magnetic tape having the total thickness of a non-magnetic layerand a magnetic layer equal to or smaller than 0.60 μm. The outputdecrease of a servo signal causes a decrease in an accuracy of theposition of the magnetic head following the data track in thetiming-based servo system (hereinafter, referred to as a “headpositioning accuracy”). Therefore, it is necessary that the outputdecrease of a servo signal is prevented, in order to more correctlyrecord information to the magnetic tape and/or more correctly reproducethe information recorded in the magnetic tape by using the timing-basedservo system.

Therefore, an object of the invention is to prevent an output decreaseof a servo signal of a timing-based servo system, in a magnetic tapehaving the total thickness of a non-magnetic layer and a magnetic layerequal to or smaller than 0.60 μm.

According to one aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; a non-magnetic layer includingnon-magnetic powder and a binder on the non-magnetic support; and amagnetic layer including ferromagnetic powder and a binder on thenon-magnetic layer, in which the total thickness of the non-magneticlayer and the magnetic layer is equal to or smaller than 0.60 μm, themagnetic layer includes a timing-based servo pattern, and logarithmicdecrement acquired by a pendulum viscoelasticity test performedregarding the surface of the magnetic layer is equal to or smaller than0.050.

The “timing-based servo pattern” of the invention and the specificationis a servo pattern with which the head tracking of the timing-basedservo system can be performed. The timing-based servo system is asdescribed above. The servo pattern with which the head tracking of thetiming-based servo system can be performed, is formed in the magneticlayer by a servo pattern recording head (also referred to as a “servowrite head”) as a plurality of servo patterns having two or moredifferent shapes. As an example, the plurality of servo patterns havingtwo or more different shapes are continuously disposed at regularintervals for each of the plurality of servo patterns having the sameshapes. As another example, different types of the servo patterns arealternately disposed. The same shapes of the servo patterns do not onlymean the completely same shape, and a shape error occurring due to adevice such as a servo write head or the like is allowed. The shapes ofthe servo pattern with which the head tracking of the timing-based servosystem can be performed and the disposition thereof in the magneticlayer are well known and specific aspect thereof will be describedlater. Hereinafter, the timing-based servo pattern is also simplyreferred to as a servo pattern. In the specification, as heads, a “servowrite head”, a “servo head”, and a “magnetic head” are disclosed. Theservo write head is a head which performs recording of a servo signal asdescribed above (that is, formation of a servo pattern). The servo headis a head which performs reproduction of the servo signal (that is,reading of the servo pattern), and the magnetic head is a head whichperforms recording and/or reproduction of information.

In one aspect, the logarithmic decrement is 0.010 to 0.050.

In one aspect, the logarithmic decrement is 0.010 to 0.040.

In one aspect, in the magnetic tape, the total thickness of thenon-magnetic layer and the magnetic layer is 0.20 μm to 0.60 μm.

According to another aspect of the invention, there is provided amagnetic tape device comprising: the magnetic tape described above; amagnetic head; and a servo head.

According to one aspect of the invention, it is possible to provide amagnetic tape in which the total thickness of a non-magnetic layer and amagnetic layer is equal to or smaller than 0.60 μm, a servo pattern isformed in a magnetic layer, and an output decrease of a servo signal ofa timing-based servo system is prevented, and a magnetic tape devicewhich records and/or reproduces a magnetic signal to the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of disposition of data bands and servo bands.

FIG. 2 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

FIG. 3 is an explanatory diagram of a measurement method of logarithmicdecrement.

FIG. 4 is an explanatory diagram of the measurement method oflogarithmic decrement.

FIG. 5 is an explanatory diagram of the measurement method oflogarithmic decrement.

FIG. 6 shows an example (step schematic view) of a specific aspect of amagnetic tape manufacturing step.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Magnetic Tape

According to one aspect of the invention, there is provided a magnetictape including: a non-magnetic support; a non-magnetic layer includingnon-magnetic powder and a binder on the non-magnetic support; and amagnetic layer including ferromagnetic powder and a binder on thenon-magnetic layer, in which the total thickness of the non-magneticlayer and the magnetic layer is equal to or smaller than 0.60 μm, themagnetic layer includes a timing-based servo pattern, and logarithmicdecrement acquired by a pendulum viscoelasticity test performedregarding the surface of the magnetic layer (hereinafter also simplyreferred to as “logarithmic decrement”) is equal to or smaller than0.050.

Hereinafter, the magnetic tape described above will be described morespecifically. The following description contains surmise of theinventors. The invention is not limited by such surmise. In addition,hereinafter, the examples are described with reference to the drawings.However, the invention is not limited to such exemplified aspects.

Timing-Based Servo Pattern

The magnetic tape includes a timing-based servo pattern in the magneticlayer. The timing-based servo pattern is the servo pattern describedabove. In a magnetic tape used in a linear recording system which iswidely used as a recording system of the magnetic tape device, forexample, a plurality of regions (referred to as “servo bands”) whereservo patterns are formed are normally present in the magnetic layeralong a longitudinal direction of the magnetic tape. A region interposedbetween two servo bands is referred to as a data band. The recording ofmagnetic signals (information) is performed on the data band and aplurality of data tracks are formed in each data band along thelongitudinal direction.

FIG. 1 shows an example of disposition of data bands and servo bands. InFIG. 1, a plurality of servo bands 10 are disposed to be interposedbetween guide bands 12 in a magnetic layer of a magnetic tape 1. Aplurality of regions 11 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in a LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 2 are formed on a servo band when manufacturing amagnetic tape. Specifically, in FIG. 2, a servo frame SF on the servoband 10 is configured with a servo sub-frame 1 (SSF1) and a servosub-frame 2 (SSF2). The servo sub-frame 1 is configured with an A burst(in FIG. 2, reference numeral A) and a B burst (in FIG. 2, referencenumeral B). The A burst is configured with servo patterns A1 to A5 andthe B burst is configured with servo patterns B1 to B5. Meanwhile, theservo sub-frame 2 is configured with a C burst (in FIG. 2, referencenumeral C) and a D burst (in FIG. 2, reference numeral D). The C burstis configured with servo patterns C1 to C4 and the D burst is configuredwith servo patterns D1 to D4. Such 18 servo patterns are disposed in thesub-frames in the arrangement of 5, 5, 4, 4, as the sets of 5 servopatterns and 4 servo patterns, and are used for recognizing the servoframes. FIG. 2 shows one servo frame for description. However, inpractice, in a magnetic layer of the magnetic tape in which a headtracking is performed in a timing-based servo system, a plurality ofservo frames are disposed in each servo band in a running direction. InFIG. 2, an arrow shows the running direction. For example, a LTO Ultriumformat tape generally includes 5,000 or more servo frames per a tapelength of 1 m, in each servo band of the magnetic layer. The servo headsequentially reads the servo patterns in the plurality of servo frames,while coming into contact with and sliding on the surface of themagnetic layer of the running magnetic tape.

In the timing-based servo system, a position of a servo head isrecognized based on an interval of time when the servo head has read thetwo servo patterns (reproduced servo signals) having different shapesand an interval of time when the servo head has read two servo patternshaving the same shapes. The time interval is normally obtained as a timeinterval of a peak of a reproduced waveform of a servo signal. Forexample, in the aspect shown in FIG. 2, the servo pattern of the A burstand the servo pattern of the C burst are servo patterns having the sameshapes, and the servo pattern of the B burst and the servo pattern ofthe D burst are servo patterns having the same shapes. The servo patternof the A burst and the servo pattern of the C burst are servo patternshaving the shapes different from the shapes of the servo pattern of theB burst and the servo pattern of the D burst. An interval of the timewhen the two servo patterns having different shapes are read by theservo head is, for example, an interval between the time when any servopattern of the A burst is read and the time when any servo pattern ofthe B burst is read. An interval of the time when the two servo patternshaving the same shapes are read by the servo head is, for example, aninterval between the time when any servo pattern of the A burst is readand the time when any servo pattern of the C burst is read. Thetiming-based servo system is a system supposing that occurrence of adeviation of the time interval is due to a position change of themagnetic tape in the width direction, in a case where the time intervalis deviated from the set value. The set value is a time interval in acase where the magnetic tape runs without occurring the position changein the width direction. In the timing-based servo system, the magnetichead is moved in the width direction in accordance with a degree of thedeviation of the obtained time interval from the set value.Specifically, as the time interval is greatly deviated from the setvalue, the magnetic head is greatly moved in the width direction. Thispoint is applied to not only the aspect shown in FIG. 1 and FIG. 2, butalso to entire timing-based servo systems. When recording andreproducing magnetic signals (information) by the magnetic head bycausing the magnetic tape to run in the magnetic tape device using thetiming-based servo system, a decrease in output of a servo signal whilecontinuously reading the servo pattern (continuously reproducing theservo signal) by the servo head causes a decrease in a measurementaccuracy of the time interval. As a result, while the running iscontinuously performed, a head positioning accuracy is decreased. Inregards to this point, in the studies of the inventors, it was foundthat the output decrease of the servo signal significantly occurs in themagnetic tape having the total thickness of the non-magnetic layer andthe magnetic layer equal to or smaller than 0.60 μm. The inventors havethought that a main reason of the output decrease of the servo signal isattached materials derived from the magnetic tape attached to a servowrite head, while a plurality of servo patterns are sequentially formedin the magnetic layer while the servo write head comes into contact withand slide on the surface of the magnetic layer of the magnetic tape. Theinventors have surmised that, as a result of deterioration of servopattern forming ability of the servo write head due to the effect of theattached materials, a magnetic force of the servo pattern formed isgradually deteriorated, while the servo patterns are continuouslyformed. It is thought that in the magnetic layer having the servopatterns formed as described above, the output of a servo signal isdecreased, while the servo patterns are continuously read by the servohead (servo signals are continuously reproduced). The inventors havesurmised that, a reason of the occurrence of such a phenomenon in themagnetic tape having the total thickness of the non-magnetic layer andthe magnetic layer equal to or smaller than 0.60 μm may be a contactstate between the servo write head and the surface of the magnetic layerof the magnetic tape which is different from that of the magnetic tapehaving the total thickness of the non-magnetic layer and the magneticlayer exceeding 0.60 μm. However, this is merely a surmise. With respectthis, as a result of the intensive studies of the inventors, it wasclear that the output decrease of the servo signal of the magnetic tapehaving the total thickness of the non-magnetic layer and the magneticlayer equal to or smaller than 0.60 μm can be prevented by setting thelogarithmic decrement to be equal to or smaller than 0.050. The surmiseof the inventors regarding this point will be described later.

Logarithmic Decrement

The logarithmic decrement acquired by a pendulum viscoelasticity testperformed regarding the surface of the magnetic layer of the magnetictape is equal to or smaller than 0.050. Accordingly, it is possible toprevent the output decrease of the servo signal in the magnetic tapehaving the total thickness of the non-magnetic layer and the magneticlayer equal to or smaller than 0.60 μm. From a viewpoint of furtherpreventing the output decrease of the servo signal, the logarithmicdecrement is preferably equal to or smaller than 0.045 and morepreferably equal to or smaller than 0.040. Meanwhile, from a viewpointof preventing the output decrease of the servo signal, it is preferablethat the logarithmic decrement is low, and therefore, the lower limitvalue is not particularly limited. The logarithmic decrement can be, forexample, equal to or greater than 0.010 or equal to or greater than0.015. However, the logarithmic decrement may be smaller than theexemplified value. A specific aspect of a method for adjusting thelogarithmic decrement will be described later. In addition, in theinvention and the specification, the “surface of the magnetic layer” isidentical to the surface of the magnetic tape on the magnetic layerside.

In the invention and the specification, the logarithmic decrement is avalue acquired by the following method.

FIG. 3 to FIG. 5 are explanatory diagrams of a measurement method of thelogarithmic decrement. Hereinafter, the measurement method of thelogarithmic decrement will be described with reference to the drawings.However, the aspect shown in the drawing is merely an example and theinvention is not limited thereto.

A measurement sample 100 is cut out from the magnetic tape which is ameasurement target. The cut-out measurement sample 100 is placed on asubstrate 103 so that a measurement surface (surface of the magneticlayer) faces upwards, in a sample stage 101 in a pendulumviscoelasticity tester, and the measurement sample is fixed by fixingtapes 105 in a state where obvious wrinkles which can be visuallyconfirmed are not generated.

A pendulum-attached columnar cylinder edge 104 (diameter of 4 mm) havingmass of 13 g is loaded on the measurement surface of the measurementsample 100 so that a long axis direction of the cylinder edge becomesparallel to a longitudinal direction of the measurement sample 100. Anexample of a state in which the pendulum-attached columnar cylinder edge104 is loaded on the measurement surface of the measurement sample 100as described above (state seen from the top) is shown in FIG. 3. In theaspect shown in FIG. 3, a holder and temperature sensor 102 is installedand a temperature of the surface of the substrate 103 can be monitored.However, this configuration is not essential. In the aspect shown inFIG. 3, the longitudinal direction of the measurement sample 100 is adirection shown with an arrow in the drawing, and is a longitudinaldirection of a magnetic tape from which the measurement sample is cutout. In addition, the description regarding angles such as “parallel” inthe specification includes a range of errors allowed in the technicalfield of the invention. For example, this means that the error is in arange within less than ±10° from an exact angle, and the error from theexact angle is preferably equal to or smaller than 5° and morepreferably equal to or smaller than 3°. In addition, as a pendulum 107(see FIG. 4), a pendulum formed of a material having properties of beingadsorbed to a magnet such as metal or an alloy is used.

The temperature of the surface of the substrate 103 on which themeasurement sample 100 is placed is set to 80° C. by increasing thetemperature at a rate of temperature increase equal to or lower than 5°C./min (arbitrary rate of temperature increase may be set, as long as itis equal to or lower than 5° C./min), and the pendulum movement isstarted (induce initial vibration) by releasing adsorption between thependulum 107 and a magnet 106. An example of a state of the pendulum 107which performs the pendulum movement (state seen from the side) is shownin FIG. 4. In the aspect shown in FIG. 4, in the pendulumviscoelasticity tester, the pendulum movement is started by stopping(switching off) the electricity to the magnet (electromagnet) 106disposed on the lower side of the sample stage to release theadsorption, and the pendulum movement is stopped by restarting(switching on) the electricity to the electromagnet to cause thependulum 107 to be adsorbed to the magnet 106. As shown in FIG. 4,during the pendulum movement, the pendulum 107 reciprocates theamplitude. From a result obtained by monitoring displacement of thependulum with a displacement sensor 108 while the pendulum reciprocatesthe amplitude, a displacement-time curve in which a vertical axisindicates the displacement and a horizontal axis indicates the elapsedtime is obtained. An example of the displacement-time curve is shown inFIG. 5. FIG. 5 schematically shows correspondence between the state ofthe pendulum 107 and the displacement-time curve. The rest (adsorption)and the pendulum movement are repeated at a regular measurementinterval, the logarithmic decrement Δ (no unit) is acquired from thefollowing Expression by using a displacement-time curve obtained in themeasurement interval after 10 minutes or longer (may be arbitrary time,as long as it is 10 minutes or longer) has elapsed, and this value isset as logarithmic decrement of the surface of the magnetic layer of themagnetic tape. The adsorption time of the first adsorption is set as 1second or longer (may be arbitrary time, as long as it is 1 second orlonger), and the interval between the adsorption stop and the adsorptionstart is set as 6 seconds or longer (may be arbitrary time, as long asit is 6 seconds or longer). The measurement interval is an interval ofthe time from the adsorption start and the nest adsorption start. Inaddition, humidity of an environment in which the pendulum movement isperformed, may be arbitrary relative humidity, as long as the relativehumidity is in a range of 40% to 70%.

$\Delta = \frac{{\ln \left( \frac{A_{1}}{A_{2\;}} \right)} + {\ln \left( \frac{A_{2}}{A_{3}} \right)} + {\ldots \mspace{14mu} {\ln \left( \frac{A_{n}}{A_{n + 1}} \right)}}}{n}$

In the displacement-time curve, an interval between a point of theminimum displacement and a point of the next minimum displacement is setas a period of a wave. n indicates the number of waves included in thedisplacement-time curve in the measurement interval, and An indicatesthe minimum displacement and maximum displacement of the n-th wave. InFIG. 5, an interval between the minimum displacement of the n-th waveand the next minimum displacement is shown as Pn (for example, P₁regarding the first wave, P₂ regarding the second wave, and P₃ regardingthe third wave). In the calculation of the logarithmic decrement, adifference (in Expression, A_(n+1), and in the displacement-time curveshown in FIG. 5, A₄) between the minimum displacement and the maximumdisplacement appearing after the n-th wave is also used, but a partwhere the pendulum 107 stops (adsorption) after the maximum displacementis not used in the counting of the number of waves. In addition, a partwhere the pendulum 107 stops (adsorption) before the maximumdisplacement is not used in the counting of the number of waves, either.Accordingly, the number of waves is 3 (n=3) in the displacement-timecurve shown in FIG. 5.

In regards to the logarithmic decrement, the inventors have consideredas follows. However, the following description is merely a surmise andthe invention is not limited thereto.

In the intensive studies of the inventors, it was found that, aphenomenon in which an output of a servo signal reproduced by a servohead is decreased compared to that in an initial running stage (outputdecrease of a servo signal) occurs, when a head tracking is continuouslyperformed while causing the surface of the magnetic layer of themagnetic tape having the total thickness of a non-magnetic layer and amagnetic layer equal to or smaller than 0.60 μm to come into contactwith and slide on the servo head, in the timing-based servo system. Theinventors have surmised that a main reason of the output decrease of theservo signal is that attached materials derived from the magnetic tapeis attached to a servo write head, while a plurality of servo patternsare sequentially formed in the magnetic layer while the servo write headcomes into contact with and slides on the surface of the magnetic layer,and servo pattern forming ability of the servo write head isdeteriorated due to the effect of the attached materials. The inventorshave surmised that the reason of the effect of the attached materialsbeing significant in the magnetic tape having the total thickness of thenon-magnetic layer and the magnetic layer equal to or smaller than 0.60μm is the contact state with the servo write head of the magnetic tapewhich is different from that of a magnetic tape having the totalthickness of the non-magnetic layer and the magnetic layer exceeding0.60 μm.

Therefore, the inventors have made further intensive research regardingthe reason of the generation of the attached materials. As a result, theinventors have newly found that the logarithmic decrement may be anindex of the amount of the attached materials derived from the magnetictape which are attached and collected on the servo write head, and bysetting the value thereof to be equal to or smaller than 0.050, it ispossible to prevent the output decrease of the servo signal.

The inventors have thought that a component to be the attached materialsderived from the magnetic tape include a viscous component separatedfrom the magnetic tape, when the servo write head and the surface of themagnetic layer come into contact with each other. The details of theviscous component are not clear. However, the inventors have surmisedthat the viscous component may be derived from a resin used as a binder.Specific description is as follows.

As a binder, various resins can be used as will be described later indetail. The resin is a polymer (including a homopolymer or a copolymer)of two or more polymerizable compounds and generally also includes acomponent having a molecular weight which is smaller than an averagemolecular weight (hereinafter, referred to as a “binder component havinga low molecular weight”). The inventors have thought that the bindercomponent having a low molecular weight which separated from themagnetic tape and attached and collected on the servo write head, whilethe servo write head continuously comes into contact with and slides onthe surface of the magnetic layer, in order to sequentially form aplurality of servo patterns in the magnetic layer, causes the outputdecrease of the servo signal, as a result. The inventors have surmisedthat, the binder component having a low molecular weight may haveviscosity and the logarithmic decrement acquired by the pendulumviscoelasticity test may be an index of the amount of the attachedmaterials attached and collected on the servo write head, while theservo write head continuously sequentially forms a plurality of servopatterns in the magnetic layer. In one aspect, the magnetic layer isformed by applying a magnetic layer forming composition including acuring agent in addition to ferromagnetic powder and a binder onto anon-magnetic support directly or with another layer interposedtherebetween, and performing curing process. With the curing processhere, it is possible to allow a curing reaction (crosslinking reaction)between the binder and the curing agent. However, the reason thereof isnot clear, and the inventors have thought that the binder componenthaving a low molecular weight may have poor reactivity regarding thecuring reaction. Accordingly, the inventors have surmised that thebinder component having a low molecular weight which hardly remains inthe magnetic layer and is easily separated from the magnetic layer andattached to the servo write head may be one of reasons for that thebinder component having a low molecular weight is easily attached andcollected on the servo write head, while the servo write headcontinuously sequentially forms a plurality of servo patterns in themagnetic layer.

However, the above-mentioned description is merely a surmise of theinventors and the invention is not limited thereto.

Hereinafter, the magnetic tape described above will be described morespecifically.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer includes ferromagnetic powder and a binder. As theferromagnetic powder, various powders normally used as ferromagneticpowder in the magnetic layer of a magnetic recording medium such as amagnetic tape can be used. It is preferable to use ferromagnetic powderhaving a small average particle size, from a viewpoint of improvement ofrecording density of the magnetic tape. From this viewpoint,ferromagnetic powder having an average particle size equal to or smallerthan 50 nm is preferably used as the ferromagnetic powder. Meanwhile,the average particle size of the ferromagnetic powder is preferablyequal to or greater than 10 nm, from a viewpoint of stability ofmagnetization.

An average particle sizes of the ferromagnetic powder is a valuemeasured by the following method with a transmission electronmicroscope.

The ferromagnetic powder is imaged at a magnification ratio of 100,000with a transmission electron microscope, and the image is printed onprinting paper so that the total magnification becomes 500,000, toobtain an image of particles configuring the ferromagnetic powder. Atarget particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetical mean of the particle size of 500particles obtained as described above is an average particle size of theferromagnetic powder. As the transmission electron microscope, atransmission electron microscope H-9000 manufactured by Hitachi, Ltd.can be used, for example. In addition, the measurement of the particlesize can be performed by well-known image analysis software, forexample, image analysis software KS-400 manufactured by Carl Zeiss.

In the invention and the specification, the average particle size of theferromagnetic powder and other powder is an average particle sizeobtained by the method described above, unless otherwise noted. Theaverage particle size shown in Examples which will be described later ismeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software.

As a method of collecting a sample powder such as ferromagnetic powderfrom the magnetic layer in order to measure the particle size, a methoddisclosed in a paragraph of 0015 of JP2011-048878A can be used, forexample.

In the invention and the specification, (1) in a case where the shape ofthe particle observed in the particle image described above is a needleshape, a fusiform shape, or a columnar shape (here, a height is greaterthan a maximum long diameter of a bottom surface), the size(hereinafter, referred to as a “particle size”) of the particlesconfiguring the powder such as ferromagnetic powder is shown as a lengthof a long axis configuring the particle, that is, a long axis length,(2) in a case where the shape of the particle is a planar shape or acolumnar shape (here, a thickness or a height is smaller than a maximumlong diameter of a plate surface or a bottom surface), the particle sizeis shown as a maximum long diameter of the plate surface or the bottomsurface, and (3) in a case where the shape of the particle is a sphereshape, a polyhedron shape, or an unspecified shape, and the long axisconfiguring the particles cannot be specified from the shape, theparticle size is shown as an equivalent circle diameter. The equivalentcircle diameter is a value obtained by a circle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of the particles ismeasured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetical mean of the values obtained regarding 500 particles iscalculated. Here, in a case of (1), the short axis length as thedefinition of the particle size is a length of a short axis configuringthe particle, in a case of (2), the short axis length is a thickness ora height, and in a case of (3), the long axis and the short axis are notdistinguished, thus, the value of (long axis length/short axis length)is assumed as 1, for convenience.

In addition, in a case where the shape of the particle is specified, forexample, in a case of definition of the particle size (1), the averageparticle size is an average long axis length, in a case of thedefinition (2), the average particle size is an average plate diameter,and an average plate ratio is an arithmetical mean of (maximum longdiameter/thickness or height). In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

As a preferred specific example of the ferromagnetic powder,ferromagnetic hexagonal ferrite powder can be used. An average particlesize of the ferromagnetic hexagonal ferrite powder (average platediameter) is preferably 10 nm to 50 nm and more preferably 20 nm to 50nm, from a viewpoint of realizing high-density recording and stabilityof magnetization. For details of the ferromagnetic hexagonal ferritepowder, descriptions disclosed in paragraphs 0012 to 0030 ofJP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, andparagraphs 0013 to 0030 of JP2012-204726A can be referred to, forexample.

As a preferred specific example of the ferromagnetic powder,ferromagnetic metal powder can also be used. An average particle size(average long axis length) of the ferromagnetic metal powder ispreferably 10 nm to 50 nm and more preferably 20 nm to 50 nm, from aviewpoint of high-density recording and stability of magnetization. Fordetails of the ferromagnetic metal powder, descriptions disclosed inparagraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 ofJP2005-251351A can be referred to, for example.

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably in a range of 50 to 90 mass % and morepreferably in a range of 60 to 90 mass %. The components other than theferromagnetic powder of the magnetic layer are at least a binder and oneor more kinds of additives may be arbitrarily included. A high fillingpercentage of the ferromagnetic powder in the magnetic layer ispreferable from a viewpoint of improvement recording density.

Binder and Curing Agent

The magnetic tape is a coating type magnetic tape, and the magneticlayer includes a binder. The binder is one or more kinds of resin. Asthe binder, various resins normally used as a binder of a coating typemagnetic recording medium can be used. For example, as the binder, aresin selected from a polyurethane resin, a polyester resin, a polyamideresin, a vinyl chloride resin, an acrylic resin obtained bycopolymerizing styrene, acrylonitrile, or methyl methacrylate, acellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin,and a polyvinylalkylal resin such as polyvinyl acetal or polyvinylbutyral can be used alone or a plurality of resins can be mixed witheach other to be used. Among these, a polyurethane resin, an acrylicresin, a cellulose resin, and a vinyl chloride resin are preferable.These resins may be a homopolymer or a copolymer. These resins can beused as the binder even in the non-magnetic layer and/or a back coatinglayer which will be described later. For the binder described above,description disclosed in paragraphs 0028 to 0031 of JP2010-24113A can bereferred to. An average molecular weight of the resin used as the bindercan be, for example, 10,000 to 200,000 as a weight-average molecularweight. The weight-average molecular weight of the invention and thespecification is a value obtained by performing polystyrene conversionof a value measured by gel permeation chromatography (GPC). As themeasurement conditions, the following conditions can be used. Theweight-average molecular weight shown in Examples which will bedescribed later is a value obtained by performing polystyrene conversionof a value measured under the following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

In addition, a curing agent can also be used together with a resin whichcan be used as the binder. As the curing agent, in one aspect, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother aspect, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinder, by proceeding the curing reaction in the magnetic layer formingstep. The preferred curing agent is a thermosetting compound,polyisocyanate is suitable. For the details of polyisocyanate,descriptions disclosed in paragraphs 0124 and 0125 of JP2011-216149A canbe referred to, for example. The amount of the curing agent can be, forexample, 0 to 80.0 parts by mass with respect to 100.0 parts by mass ofthe binder in the magnetic layer forming composition, and is preferably50.0 to 80.0 parts by mass, from a viewpoint of improvement of strengthof each layer such as the magnetic layer.

Additive

The magnetic layer includes the ferromagnetic powder and the binder, andmay include one or more kinds of additives, if necessary. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include a non-magnetic filler, a lubricant, a dispersing agent, adispersing assistant, an antibacterial agent, an antistatic agent, anantioxidant, and carbon black. As the additives, a commerciallyavailable product can be suitably selected and used according to desiredproperties.

Hereinafter, a non-magnetic filler which is one aspect of the additivewill be described. However, the invention is not limited to thefollowing aspect. The non-magnetic filler is identical to thenon-magnetic powder. In addition, in the invention and thespecification, the non-magnetic powder means an aggregate of a pluralityof non-magnetic particles. The aggregate not only includes an aspect inwhich particles configuring the aggregate directly come into contactwith each other, and also includes an aspect in which a binder and anadditive is interposed between the particles. A term “particles” is alsoused for describing the powder. The same applies to various powders ofthe invention and the specification.

It is preferable that the magnetic layer includes one kind or two ormore kinds of the non-magnetic filler. As the non-magnetic filler, anon-magnetic filler (hereinafter, referred to as a “projection formationagent”) which can function as a projection formation agent which formsprojections suitably protruded from the surface of the magnetic layer,and a non-magnetic filler (hereinafter, referred to as an “abrasive”)which can function as an abrasive can be used. The projection formationagent is a component which can contribute to the control of frictionproperties of the surface of the magnetic layer. It is preferable thatat least one of the projection formation agent and the abrasive isincluded in the magnetic layer of the magnetic tape, and it ispreferable that both of them are included.

As the projection formation agent, various non-magnetic fillers normallyused as a projection formation agent can be used. These may be inorganicsubstances or organic substances. In one aspect, from a viewpoint ofhomogenization of friction properties, particle size distribution of theprojection formation agent is not polydispersion having a plurality ofpeaks in the distribution and is preferably monodisperse showing asingle peak. From a viewpoint of availability of monodisperse particles,the non-magnetic filler is preferably powder of inorganic substances.Examples of the powder of inorganic substances include powder of metaloxide, metal carbonate, metal sulfate, metal nitride, metal carbide, andmetal sulfide, and powder of inorganic oxide is preferable. Theprojection formation agent is more preferably colloidal particles andeven more preferably inorganic oxide colloidal particles. In addition,from a viewpoint of availability of monodisperse particles, theinorganic oxide configuring the inorganic oxide colloidal particles arepreferably silicon dioxide (silica). The inorganic oxide colloidalparticles are more preferably colloidal silica (silica colloidalparticles). The average particle size of the colloidal particles is avalue obtained by a method disclosed in a paragraph 0015 ofJP2011-048878A as a measurement method of an average particle diameter.In addition, in another aspect, the projection formation agent ispreferably carbon black.

An average particle size of the projection formation agent is, forexample, 30 to 300 nm and is preferably 40 to 200 nm.

Meanwhile, as the abrasive, powders of alumina (Al₂O₃), silicon carbide,boron carbide (B₄C), SiO₂, TiC chromium oxide (Cr₂O₃), cerium oxide,zirconium oxide (ZrO₂), iron oxide, diamond, and the like which aresubstances normally used as the abrasive of the magnetic layer can beused, and among these, alumina powder such as α-alumina and siliconcarbide powder are preferable. In addition, regarding the particle sizeof the abrasive, a specific surface area which is an index of theparticle size is, for example, equal to or greater than 14 m²/g, and ispreferably 16 m²/g and more preferably 18 m²/g. Further, the specificsurface area of the abrasive can be, for example, equal to or smallerthan 40 m²/g. The specific surface area is a value obtained by anitrogen adsorption method (also referred to as a Brunauer-Emmett-Teller(BET) 1 point method), and is a value measured regarding primaryparticles. Hereinafter, the specific surface area obtained by such amethod is also referred to as a BET specific surface area.

In addition, from a viewpoint that the projection formation agent andthe abrasive can exhibit the functions thereof in more excellent manner,the content of the projection formation agent of the magnetic layer ispreferably 1.0 to 4.0 parts by mass and more preferably 1.5 to 3.5 partsby mass with respect to 100.0 parts by mass of the ferromagnetic powder.Meanwhile, the content of the abrasive in the magnetic layer ispreferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 partsby mass, and even more preferably 4.0 to 10.0 parts by mass with respectto 100.0 parts by mass of the ferromagnetic powder.

As an example of the additive which can be used in the magnetic layerincluding the abrasive, a dispersing agent disclosed in paragraphs 0012to 0022 of JP2013-131285A can be used as a dispersing agent forimproving dispersibility of the abrasive.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape maydirectly include a magnetic layer on a non-magnetic support, or mayinclude a magnetic layer on a non-magnetic support with at least anotherlayer interposed therebetween. Such another layer is preferably anon-magnetic layer including non-magnetic powder and a binder. Thenon-magnetic powder used in the non-magnetic layer may be inorganicsubstances or organic substances. In addition, carbon black and the likecan be used. Examples of the inorganic substances include metal, metaloxide, metal carbonate, metal sulfate, metal nitride, metal carbide, andmetal sulfide. The non-magnetic powder can be purchased as acommercially available product or can be manufactured by a well-knownmethod. For details thereof, descriptions disclosed in paragraphs 0146to 0150 of JP2011-216149A can be referred to. For carbon black which canbe used in the non-magnetic layer, descriptions disclosed in paragraphs0040 and 0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably in a range of 50 to 90 mass % and more preferably in a rangeof 60 to 90 mass %.

In regards to other details of a binder or additives of the non-magneticlayer, the well-known technology regarding the non-magnetic layer can beapplied. In addition, in regards to the type and the content of thebinder, and the type and the content of the additive, for example, thewell-known technology regarding the magnetic layer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support (hereinafter, also simply referred to asa “support”) will be described. As the non-magnetic support, well-knowncomponents such as polyethylene terephthalate, polyethylene naphthalate,polyamide, polyamide imide, aromatic polyamide subjected to biaxialstretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or thermaltreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binder on a side of the non-magnetic supportopposite to the side including the magnetic layer. The back coatinglayer preferably includes any one or both of carbon black and inorganicpowder. In regards to the binder included in the back coating layer andvarious additives which can be arbitrarily included in the back coatinglayer, a well-known technology regarding the treatment of the magneticlayer and/or the non-magnetic layer can be applied.

Various Thickness

In the magnetic tape, the total thickness of the magnetic layer and thenon-magnetic layer is equal to or smaller than 0.60 μm and preferablyequal to or smaller than 0.50 μm, from a viewpoint of thinning themagnetic tape. In addition, the total thickness of the magnetic layerand the non-magnetic layer is, for example, equal to or greater than0.10 μm or equal to or greater than 0.20 μm.

In the thicknesses of the non-magnetic support and each layer of themagnetic tape, the thickness of the non-magnetic support is preferably3.00 to 4.50 μm.

A thickness of the magnetic layer can be optimized in accordance withsaturation magnetization quantity of the magnetic head used, a head gaplength, or a band of a recording signal. The thickness of the magneticlayer is normally 0.01 μm to 0.15 μm, and is preferably 0.02 μm to 0.12μm and more preferably 0.03 μm to 0.10 μm, from a viewpoint of realizingrecording at high density. The magnetic layer may be at least singlelayer, the magnetic layer may be separated into two or more layershaving different magnetic properties, and a configuration of awell-known multilayered magnetic layer can be applied. A thickness ofthe magnetic layer in a case where the magnetic layer is separated intotwo or more layers is the total thickness of the layers.

The thickness of the non-magnetic layer is, for example, 0.10 to 0.55 μmand is preferably 0.10 to 0.50 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.90 μm and even more preferably in a range of 0.10 to 0.70 μm.

In addition, the total thickness of the magnetic tape is preferablyequal to or smaller than 6.00 μm, more preferably equal to or smallerthan 5.70 μm, and even more preferably equal to or smaller than 5.50 μm,from a viewpoint of improving recording capacity for 1 magnetic tapecartridge. Meanwhile, the total thickness of the magnetic tape ispreferably equal to or greater than 1.00 μm, from a viewpoint ofavailability (handling properties) of the magnetic tape.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scan electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are arbitrarilyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Measurement Method

Manufacturing of Magnetic Tape in which Servo Pattern is Formed

Preparation of Each Layer Forming Composition

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, organic solventsgenerally used for manufacturing a coating type magnetic recordingmedium can be used. Among those, from a viewpoint of solubility of thebinder normally used in the coating type magnetic recording medium, eachlayer forming composition preferably includes one or more ketonesolvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone,diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran. Theamount of the solvent of each layer forming composition is notparticularly limited, and can be set to be the same as that of eachlayer forming composition of a typical coating type magnetic recordingmedium.

The steps of preparing each layer forming composition generally includeat least a kneading step, a dispersing step, and a mixing step providedbefore and after these steps, if necessary. Each step may be dividedinto two or more stages. All of raw materials used in the invention maybe added at an initial stage or in a middle stage of each step. Inaddition, each raw material may be separately added in two or moresteps. For example, in the preparation of the magnetic layer formingcomposition, it is preferable that the abrasive and the ferromagneticpowder are separately dispersed. In the kneading step, an open kneader,a continuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder is preferably used. The details ofthe kneading processes of these kneaders are disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). In addition, inorder to disperse each layer forming composition, glass beads and/orother beads can be used. As such dispersion beads, zirconia beads,titania beads, and steel beads which are dispersion beads having highspecific gravity are suitable. These dispersion beads are preferablyused by optimizing a bead diameter and a filling percentage. As adispersion device, a well-known dispersion device can be used.

Coating Step, Cooling Step, Heating and Drying Step, BurnishingTreatment Step, and Curing Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the non-magnetic support or preferably byperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. For details of the coating for forming each layer, a descriptiondisclosed in a paragraph 0066 of JP2010-231843A can be referred to.

In a preferred aspect, a magnetic layer can be formed through a magneticlayer forming step including a coating step of applying a magnetic layerforming composition including ferromagnetic powder, a binder, a curingagent, and a solvent onto a non-magnetic support directly or withanother layer interposed therebetween, to form a coating layer, aheating and drying step of drying the coating layer by a heatingprocess, and a curing step of performing a curing process with respectto the coating layer. The magnetic layer forming step preferablyincludes a cooling step of cooling the coating layer between the coatingstep and the heating and drying step, and more preferably includes aburnishing treatment step of performing a burnishing treatment withrespect to the surface of the coating layer between the heating anddrying step and the curing step.

The inventors have thought that it is preferable that the cooling stepand the burnishing treatment step in the magnetic layer forming step, inorder to set the logarithmic decrement to be equal to or smaller than0.050. More specific description is as follows.

The inventors have surmised that performing the cooling step of coolingthe coating layer between the coating step and the heating and dryingstep contributes viscous component separated from the magnetic tape whenthe servo write head comes into contact with and slides on the surfaceof the magnetic layer, which is localized in the surface and/or asurface layer part in the vicinity of the surface of the coating layer.The inventors have surmised that this is because the viscous componentat the time of solvent volatilization in the heating and drying step iseasily moved to the surface and/or the surface layer part of the coatinglayer, by cooling the coating layer of the magnetic layer formingcomposition before the heating and drying step. However, the reasonthereof is not clear. In addition, the inventors have thought that theviscous component can be removed by performing the burnishing treatmentwith respect to the surface of the coating layer in which the viscouscomponent is localized on the surface and/or surface layer part. Theinventors have surmised that performing the curing step after removingthe viscous component contributes setting the logarithmic decrement tobe equal to or smaller than 0.050. However, this is merely a surmise,and the invention is not limited thereto.

As described above, multilayer coating of the magnetic layer formingcomposition can be performed with the non-magnetic layer formingcomposition in order or at the same time. In a preferred aspect, themagnetic tape can be manufactured by successive multilayer coating. Amanufacturing step including the successive multilayer coating can bepreferably performed as follows. The non-magnetic layer is formedthrough a coating step of applying a non-magnetic layer formingcomposition onto a non-magnetic support to form a coating layer, and aheating and drying step of drying the formed coating layer by a heatingprocess. In addition, the magnetic layer is formed through a coatingstep of applying a magnetic layer forming composition onto the formednon-magnetic layer to form a coating layer, and a heating and dryingstep of drying the formed coating layer by a heating process.

Hereinafter, a specific aspect of the manufacturing method of themagnetic tape will be described with reference to FIG. 6. However, theinvention is not limited to the following specific aspect.

FIG. 6 is a step schematic view showing a specific aspect of a step ofmanufacturing the magnetic tape including a non-magnetic layer and amagnetic layer in this order on one surface of a non-magnetic supportand including a back coating layer on the other surface thereof. In theaspect shown in FIG. 6, an operation of sending a non-magnetic support(elongated film) from a sending part and winding the non-magneticsupport around a winding part is continuously performed, and variousprocesses of coating, drying, and orientation are performed in each partor each zone shown in FIG. 6, and thus, it is possible to sequentiallyform a non-magnetic layer and a magnetic layer on one surface of therunning non-magnetic support by multilayer coating and to form a backcoating layer on the other surface thereof. Such a manufacturing methodcan be set to be identical to the manufacturing method normallyperformed for manufacturing a coating type magnetic recording medium,except for including a cooling zone in the magnetic layer forming stepand including the burnishing treatment step before the curing process.

The non-magnetic layer forming composition is applied onto thenon-magnetic support sent from the sending part in a first coating part(coating step of non-magnetic layer forming composition).

After the coating step, in a first heating process zone, the coatinglayer of the non-magnetic layer forming composition formed in thecoating step is heated after to dry the coating layer (heating anddrying step). The heating and drying step can be performed by causingthe non-magnetic support including the coating layer of the non-magneticlayer forming composition to pass through the heated atmosphere. Anatmosphere temperature of the heated atmosphere here can be, forexample, approximately 60° C. to 140° C. Here, the atmospheretemperature may be a temperature at which the solvent is volatilized andthe coating layer is dried, and the atmosphere temperature is notlimited to the range described above. In addition, the heated air mayblow to the surface of the coating layer. The points described above arealso applied to a heating and drying step of a second heating processzone and a heating and drying step of a third heating process zone whichwill be described later, in the same manner.

Next, in a second coating part, the magnetic layer forming compositionis applied onto the non-magnetic layer formed by performing the heatingand drying step in the first heating process zone (coating step ofmagnetic layer forming composition).

After the coating step, a coating layer of the magnetic layer formingcomposition formed in the coating step is cooled in a cooling zone(cooling step). For example, it is possible to perform the cooling stepby allowing the non-magnetic support on which the coating layer isformed on the non-magnetic layer to pass through a cooling atmosphere.An atmosphere temperature of the cooling atmosphere is preferably in arange of −10° C. to 0° C. and more preferably in a range of −5° C. to 0°C. The time for performing the cooling step (for example, time while anarbitrary part of the coating layer is delivered to and sent from thecooling zone (hereinafter, also referred to as a “staying time”)) is notparticularly limited. When the staying time is long, the value oflogarithmic decrement tends to be increased. Thus, the staying time ispreferably adjusted by performing preliminary experiment if necessary,so that the logarithmic decrement equal to or smaller than 0.050 isrealized. In the cooling step, cooled air may blow to the surface of thecoating layer.

After that, while the coating layer of the magnetic layer formingcomposition is wet, an orientation process of the ferromagnetic powderin the coating layer is performed in an orientation zone. For theorientation process, a description disclosed in a paragraph 0067 ofJP2010-231843A can be referred to.

The coating layer after the orientation process is subjected to theheating and drying step in the second heating process zone.

Next, in the third coating part, a back coating layer formingcomposition is applied to a surface of the non-magnetic support on aside opposite to the surface where the non-magnetic layer and themagnetic layer are formed, to form a coating layer (coating step of backcoating layer forming composition). After that, the coating layer isheated and dried in the third heating process zone.

By doing so, it is possible to obtain the magnetic tape including thecoating layer of the magnetic layer forming composition heated and driedon the non-magnetic layer, on one surface side of the non-magneticsupport, and the back coating layer on the other surface side thereof.The magnetic tape obtained here becomes a magnetic tape product afterperforming various processes which will be described later.

The obtained magnetic tape is wound around the winding part, and cut(slit) to have a size of a magnetic tape product. The slitting isperformed by using a well-known cutter.

In the slit magnetic tape, the burnishing treatment is performed withrespect to the surface of the heated and dried coating layer of themagnetic layer forming composition, before performing the curing process(heating and light irradiation) in accordance with the types of thecuring agent included in the magnetic layer forming composition(burnishing treatment step between heating and drying step and curingstep). The inventors have surmised that removing the viscous componenttransitioned to the surface and/or the surface layer part of the coatinglayer cooled in the cooling zone by the burnishing treatment contributessetting the logarithmic decrement to be equal to or smaller than 0.050.However, as described above, this is merely a surmise, and the inventionis not limited thereto.

The burnishing treatment is treatment of rubbing a surface of atreatment target with a member (for example, a polishing tape, or agrinding tool such as a grinding blade or a grinding wheel), and can beperformed in the same manner as the well-known burnishing treatment formanufacturing a coating type magnetic recording medium. However, in therelated art, the burnishing treatment was not performed in a stagebefore the curing step, after performing the cooling step and theheating and drying step. With respect to this, the logarithmic decrementcan be equal to or smaller than 0.050 by performing the burnishingtreatment in the stage described above. This point was newly found bythe inventors.

The burnishing treatment can be preferably performed by performing oneor both of rubbing of the surface of the coating layer of the treatmenttarget by a polishing tape (polishing) and rubbing of the surface of thecoating layer of the treatment target by a grinding tool (grinding). Ina case where the magnetic layer forming composition includes anabrasive, it is preferable to use a polishing tape including at leastone kind of an abrasive having higher Mohs hardness than that of theabrasive described above. As the polishing tape, a commerciallyavailable product may be used and a polishing tape manufactured by awell-known method may be used. As the grinding tool, a well-known bladesuch as a fixed blade, a diamond wheel, or a rotary blade, or a grindingblade can be used. In addition, a wiping treatment of wiping the surfaceof the coating layer rubbed by the polishing tape and/or the grindingtool with a wiping material. For details of preferred polishing tape,grinding tool, burnishing treatment, and wiping treatment, descriptionsdisclosed in paragraphs 0034 to 0048, FIG. 1 and Examples ofJP1994-52544A (JP-1106-52544A) can be referred to. As the burnishingtreatment is reinforced, the value of the logarithmic decrement tends tobe decreased. The burnishing treatment can be reinforced as an abrasivehaving high hardness is used as the abrasive included in the polishingtape, and can be reinforced, as the amount of the abrasive in thepolishing tape is increased. In addition, the burnishing treatment canbe reinforced as a grinding tool having high hardness is used as thegrinding tool. In regards to the burnishing treatment conditions, theburnishing treatment can be reinforced as a sliding speed between thesurface of the coating layer of the treatment target and a member (forexample, a polishing tape or a grinding tool) is increased. The slidingspeed can be increased by increasing one or both of a speed at which themember is moved, and a speed at which the magnetic tape of the treatmenttarget is moved.

After the burnishing treatment (burnishing treatment step), the curingprocess is performed with respect to the coating layer of the magneticlayer forming composition. In the aspect shown in FIG. 6, the coatinglayer of the magnetic layer forming composition is subjected to thesurface smoothing treatment, after the burnishing treatment and beforethe curing process. The surface smoothing treatment is preferablyperformed by a calender process. For details of the calender process,for example, description disclosed in a paragraph 0026 of JP2010-231843Acan be referred to. As the calender process is reinforced, the surfaceof the magnetic tape can be smoothened. The calender process isreinforced, as the surface temperature (calender temperature) of acalender roll is increased and/or as calender pressure is increased.

After that, the curing process according to the type of the curing agentincluded in the coating layer is performed with respect to the coatinglayer of the magnetic layer forming composition (curing step). Thecuring process can be performed by the process according to the type ofthe curing agent included in the coating layer, such as a heatingprocess or light irradiation. The curing process conditions are notparticularly limited, and the curing process conditions may be suitablyset in accordance with the list of the magnetic layer formingcomposition used in the coating layer formation, the type of the curingagent, and the thickness of the coating layer. For example, in a casewhere the coating layer is formed by using the magnetic layer formingcomposition including polyisocyanate as the curing agent, the curingprocess is preferably the heating process. In a case where the curingagent is included in a layer other than the magnetic layer, a curingreaction of the layer can also be promoted by the curing process here.Alternatively, the curing step may be separately provided. After thecuring step, the burnishing treatment may be further performed.

As described above, it is possible to obtain a magnetic tape havinglogarithmic decrement equal to or smaller than 0.050 which is acquiredby pendulum viscoelasticity test performed regarding the surface of themagnetic layer of the magnetic tape. However, the manufacturing methoddescribed above is merely an example, the logarithmic decrement equal toor smaller than 0.050 can be realized by an arbitrary method capable ofadjusting the logarithmic decrement, and such an aspect is also includedin the invention.

Formation of Servo Pattern

The magnetic tape includes a timing-based servo pattern in the magneticlayer. FIG. 1 shows a disposition example of a region (servo band) inwhich the timing-based servo pattern is formed and a region (data band)interposed between two servo bands. FIG. 2 shows a disposition exampleof the timing-based servo patterns. Here, the disposition example shownin each drawing is merely an example, and the servo pattern, the servobands, and the data bands may be disposed in the disposition accordingto a system of the magnetic tape device (drive). In addition, for theshape and the disposition of the timing-based servo pattern, awell-known technology such as disposition examples shown in FIG. 4, FIG.5, FIG. 6, FIG. 9, FIG. 17, and FIG. 20 of U.S. Pat. No. 5,689,384A canbe applied without any limitation, for example.

The servo pattern can be formed by magnetizing a specific region of themagnetic layer by a servo write head mounted on a servo writer. A regionto be magnetized by the servo write head (position where the servopattern is formed) is determined by standards. As the servo writer, acommercially available servo writer or a servo writer having awell-known configuration can be used. For the configuration of the servowriter, well-known technologies such as technologies disclosed inJP2011-175687A, U.S. Pat. No. 5,689,384A, and U.S. Pat. No. 6,542,325Bcan be referred to without any limitation.

The magnetic tape according to one aspect of the invention describedabove is a magnetic tape in which the total thickness of a non-magneticlayer and a magnetic layer is equal to or smaller than 0.60 μm and servopatterns are formed in the magnetic layer, and can prevent the outputdecrease of the servo signal of the timing-based servo system.

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape device includingthe magnetic tape, a magnetic head, and a servo head.

The details of the magnetic tape mounted on the magnetic tape device areas described above. The magnetic tape is generally accommodated in amagnetic tape cartridge and the magnetic tape cartridge is attached tothe magnetic tape device. Details of the structure of the magnetic tapecartridge are well known. The magnetic tape cartridge is mounted on themagnetic tape device. The magnetic tape includes timing-based servopatterns. Accordingly, a magnetic signal is recorded on the data band bythe magnetic head to form a data track, and/or, when reproducing therecorded signal, a head tracking of a timing-based servo type can beperformed based on the read servo pattern, while reading the servopattern by the servo head. Here, when the output of the servo signal isdecreased, the head positioning accuracy may be decreased, as describedabove. With respect to this, according to the magnetic tape, it ispossible to prevent the output decrease of the servo signal, andaccordingly, it is possible to cause the magnetic head to follow thedata track at a high accuracy in the timing-based servo system.

As the magnetic head mounted on the magnetic tape device, a well-knownmagnetic head which can perform the recording and/or reproducing of themagnetic signal with respect to the magnetic tape can be used. Arecording head and a reproduction head may be one magnetic head or maybe separated magnetic heads. As the servo head, a well-known servo headwhich can read the timing-based servo pattern of the magnetic tape canbe used. At least one or two or more servo heads may be included in themagnetic tape device.

For details of the head tracking of the timing-based servo system, forexample, well-known technologies such as technologies disclosed in U.S.Pat. No. 5,689,384A, U.S. Pat. No. 6,542,325B, and U.S. Pat. No.7,876,521B can be used without any limitation.

A commercially available magnetic tape device generally includes amagnetic head and a servo head in accordance to a standard. In addition,a commercially available magnetic tape device generally has a servocontrolling mechanism for realizing head tracking of the timing-basedservo system in accordance to a standard. The magnetic tape deviceaccording to one aspect of the invention can be configured byincorporating the magnetic tape according to one aspect of the inventionto a commercially available magnetic tape device.

EXAMPLES

Hereinafter, the invention will be described with reference to Examples.However, the invention is not limited to aspects shown in the Examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted.

Examples 1 to 7 and Comparative Examples 1 to 6

1. Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin having a SO₃Na group as a polar group (UR-4800 (amount of a polargroup: 80 meq/kg) manufactured by Toyobo Co., Ltd.), and 570.0 parts ofa mixed solution of methyl ethyl ketone and cyclohexanone (mass ratio of1:1) as a solvent were mixed in 100.0 parts of alumina powder (HIT-80manufactured by Sumitomo Chemical Co., Ltd.) having an gelatinizationratio of 65% and a BET specific surface area of 20 m²/g, and dispersedin the presence of zirconia beads by a paint shaker for 5 hours. Afterthe dispersion, the dispersion liquid and the beads were separated by amesh and an alumina dispersion was obtained.

2. Magnetic Layer Forming Composition List

Magnetic Solution

Ferromagnetic powder: see Table 1: 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive liquid

Alumina dispersion prepared in the section 1.: 6.0 parts

Silica Sol

Colloidal silica

Average particle size: 80 nm: 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE (registered trademark) L manufactured by NipponPolyurethane Industry): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

In Table 1, BF indicates ferromagnetic hexagonal barium ferrite powderhaving an average particle size (average plate diameter) of 21 nm, andMP indicates ferromagnetic metal powder having an average particle size(average long axis length) of 30 nm.

3. Non-Magnetic Layer Forming Composition List

Non-magnetic inorganic powder: α-iron oxide: 100.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

Vinyl chloride copolymer: 13.0 parts

SO₃Na group-containing polyurethane resin: 9.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Phenylphosphonic acid: 3.0 parts

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

4. Back Coating Layer Forming Composition List

Non-magnetic inorganic powder: α-iron oxide: 80.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

Vinyl chloride copolymer: 13.0 parts

SO₃Na group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Methyl ethyl ketone: 155.0 parts

Stearic acid: 3.0 parts

Butyl stearate: 3.0 parts

Polyisocyanate: 5.0 parts

Cyclohexanone: 355.0 parts

5. Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod. The magnetic solution was prepared by dispersing(beads-dispersing) each component with a batch type vertical sand millfor 24 hours. As the dispersion beads, zirconia beads having a beaddiameter of 0.1 mm were used. The prepared magnetic solution and theabrasive liquid were mixed with other components (silica sol, othercomponents, and finishing additive solvent) and beads-dispersed for 5minutes by using the sand mill, and a process (ultrasonic dispersion)was performed with a batch type ultrasonic device (20 kHz, 300 W) for0.5 minutes. After that, the filtering was performed by using a filterhaving an average hole diameter of 0.5 μm, and the magnetic layerforming composition was prepared.

The non-magnetic layer forming composition was prepared by the followingmethod. Each component excluding a lubricant (stearic acid, stearic acidamide, and butyl stearate), cyclohexanone, and methyl ethyl ketone wasdispersed by using batch type vertical sand mill for 24 hours to obtaindispersion liquid. As the dispersion beads, zirconia beads having a beaddiameter of 0.1 mm were used. After that, the remaining components wereadded into the obtained dispersion liquid and stirred with a dissolver.The dispersion liquid obtained as described above was filtered with afilter having an average hole diameter of 0.5 μm and a non-magneticlayer forming composition was prepared.

The back coating layer forming composition was prepared by the followingmethod. Each component excluding the lubricant (stearic acid and butylstearate), polyisocyanate, and cyclohexanone was kneaded and diluted byan open kneader, and subjected to a dispersing process of 12 passes,with a transverse beads mill dispersion device and zirconia beads havinga bead diameter of 1 mm, by setting a bead filling percentage as 80volume %, a circumferential speed of rotor tip as 10 m/sec, and aretention time for 1 pass as 2 minutes. After that, the remainingcomponents were added into the obtained dispersion liquid and stirredwith a dissolver. The dispersion liquid obtained as described above wasfiltered with a filter having an average hole diameter of 1 μm and aback coating layer forming composition was prepared.

6. Manufacturing of Magnetic Tape in which Servo Patterns are Formed

The magnetic tape was manufactured by a specific aspect shown in FIG. 6.The magnetic tape was specifically manufactured as follows.

A support made of polyethylene naphthalate having a thickness shown inTable 1 was sent from the sending part, and the non-magnetic layerforming composition prepared in the section 5. was applied to onesurface thereof so that the thickness after the drying becomes thethickness shown in Table 1 in the first coating part and was dried inthe first heating process zone (atmosphere temperature of 100° C.) toform a coating layer.

Then, the magnetic layer forming composition prepared in the section 5.was applied onto the non-magnetic layer so that the thickness after thedrying became the thickness shown in Table 1 in the second coating part,and a coating layer was formed. The cooling step was performed bypassing the formed coating layer through the cooling zone in which theatmosphere temperature is adjusted to 0° C. for the staying time shownin Table 1 while the coating layer is wet, a vertical alignment processwas performed in the orientation zone by applying a magnetic fieldhaving a magnetic field strength of 0.3 T in a vertical direction, andthen, the coating layer was dried in the second heating process zone(atmosphere temperature of 100° C.) at an atmosphere temperature of 100°C.

After that, in the third coating part, the back coating layer formingcomposition prepared in the section 5. was applied to the surface of thesupport made of polyethylene naphthalate on a side opposite to thesurface where the non-magnetic layer and the magnetic layer were formed,so that the thickness after the drying became the thickness shown inTable 1, to form a coating layer, and the formed coating layer was driedin the third heating process zone (atmosphere temperature of 100° C.).

The magnetic tape obtained as described above was slit to have a widthof ½ inches (0.0127 meters), and the burnishing treatment and the wipingtreatment were performed with respect to the surface of the coatinglayer of the magnetic layer forming composition. The burnishingtreatment and the wiping treatment were performed by using acommercially available polishing tape (product name: MA22000manufactured by Fujifilm Holdings Corporation, abrasive:diamond/Cr₂O₃/red oxide) as the polishing tape, a commercially availablesapphire blade (manufactured by Kyocera Corporation, a width of 5 mm, alength of 35 mm, and a tip angle of 60 degrees) as the grinding blade,and a commercially available wiping material (product name: WRP736manufactured by Kuraray Co., Ltd) as the wiping material, in a treatmentdevice having a configuration disclosed in FIG. 1 of JP1994-52544A(JP-1106-52544A). For the treatment conditions, the treatment conditionsdisclosed in Example 12 of JP1994-52544A (JP-1106-52544A).

After the burnishing treatment and the wiping treatment, a calenderprocess (surface smoothing treatment) was performed with a calender rollconfigured of only a metal roll, at a speed of 80 m/min, linear pressureof 300 kg/cm (294 kN/m), and a surface temperature of a calender roll of95° C.

Then, the curing process (heating process) was performed in theenvironment of the atmosphere temperature of 70° C. for 36 hours toobtain a magnetic tape.

In Table 1, in the Comparative Examples in which “not performed” isdisclosed in a column of the cooling zone staying time, a magnetic tapewas manufactured by a manufacturing step not including a cooling zone.

In Table 1, in the Comparative Examples in which “not performed” isdisclosed in a column of the burnishing treatment before the curingstep, a magnetic tape was manufactured by a manufacturing step of notperforming the burnishing treatment and the subsequent wiping treatmentin the step before performing the curing process.

In Table 1, in Comparative Example 6 in which “performed” is disclosedin a column of the burnishing treatment before the curing step, theburnishing treatment and the wiping treatment described above werecontinuously repeated 10 times in the step after performing the curingprocess.

By performing the steps described above, the magnetic tape wasmanufactured.

7. Formation of Timing-Based Servo Pattern

In a state where the magnetic layer of the manufactured magnetic tapewas demagnetized, servo patterns having disposition and shapes accordingto the LTO Ultrium format were formed on the magnetic layer by using aservo write head mounted on a servo testing machine. Accordingly, amagnetic tape including data bands, servo bands, and guide bands in thedisposition according to the LTO Ultrium format in the magnetic layer,and including servo patterns having the disposition and the shapeaccording to the LTO Ultrium format on the servo band is obtained. Inthis magnetic tape, total 5,000,000 servo frames of servo framesincluding the A burst, B burst, C burst, and D burst are formed in thedisposition shown in FIG. 2. The servo testing machine includes a servowrite head and a servo head. This servo testing machine was also used inthe evaluation which will be described later.

By performing the steps described above, each magnetic tape of Examplesand Comparative Examples in which a timing-based servo pattern is formedin a magnetic layer was obtained. The following evaluation of theobtained each magnetic tape was performed.

The thickness of each layer and the non-magnetic support of eachmagnetic tape obtained as described above was acquired by the followingmethod. It was confirmed that each layer and the non-magnetic supportformed have the thickness shown in Table 1.

The cross section of the magnetic tape in a thickness direction wasexposed by an ion beam, and then, the cross section observation of theexposed cross section was performed with a scanning electron microscope.Various thicknesses were acquired as an arithmetical mean of thicknessesacquired at two positions in the thickness direction, in the crosssection observation.

Evaluation Method

1. Measurement of Logarithmic Decrement

The logarithmic decrement of the surface of the magnetic layer of eachmagnetic tape of Examples and Comparative Examples was acquired by themethod described above by using a rigid-body pendulum type physicalproperties testing instrument RPT-3000W (pendulum: brass, substrate:glass substrate, a rate of temperature increase of substrate: 5° C./min)as the measurement device. A measurement sample cut out from eachmagnetic tape of Examples and Comparative Examples was placed on a glasssubstrate having a size of approximately 3 cm×approximately 5 cm, bybeing fixed at 4 portions with a fixing tape (Kapton tape manufacturedby Du Pont-Toray Co., Ltd.) as shown in FIG. 3. An adsorption time wasset as 1 second, a measurement interval was set as 7 to 10 seconds, adisplacement-time curve was drawn regarding the 86-th measurementinterval, and the logarithmic decrement was acquired by using thiscurve. The measurement was performed in the environment of relativehumidity of approximately 50%.

2. Output Decreased Amount of Servo Signal

The magnetic tape in which the timing-based servo pattern is formed wasattached to a servo testing machine. In the servo testing machine, theservo patterns were sequentially read (servo signals were reproduced) bythe servo head from the servo pattern of the first servo frame formed inthe magnetic tape to the servo pattern of the final 5,000,000-th servoframe, while bringing the surface of the magnetic layer of the runningmagnetic tape to come into contact with and slide on the servo head. Anarithmetical mean of the signal output obtained in the first to 100-thservo frames was set as A, an arithmetical mean of the signal outputobtained in the 4,999,900-th to 5,000,000-th servo frames was set as B,and the output decreased amount of the servo signal (unit: %) wascalculated with an expression of “[(B−A)/A]×100”.

The results described above are shown in Table 1.

TABLE 1 Comparative Comparative Comparative Comparative ComparativeComparative Example Example 1 Example 2 Example 3 Example 4 Example 5Example 6 1 Ferromagnetic powder BF BF BF BF MP BF BF Magnetic layerthickness μm 0.10 0.10 0.10 0.10 0.10 0.10 0.10 Non-magnetic layer μm1.00 0.70 0.50 0.10 0.50 0.50 0.50 thickness Non-magnetic support μm4.30 4.30 4.30 4.30 4.30 4.30 4.30 thickness Back coating layer μm 0.600.60 0.60 0.60 0.60 0.60 0.60 thickness Total thickness of μm 1.10 0.800.60 0.20 0.60 0.60 0.60 non-magnetic layer + magnetic layer Coolingzone staying Not Not Not Not Not Not 1 second time performed performedperformed performed performed performed Burnishing treatment Not Not NotNot Not Not Performed before curing step performed performed performedperformed performed performed Burnishing treatment Not Not Not Not NotPerformed Not after curing step performed performed performed performedperformed performed Logarithmic decrement 0.062 0.061 0.062 0.063 0.0720.056 0.048 of magnetic layer Servo signal output % −0.30 −0.60 −2.80−43.00 −8.20 −3.40 −1.00 decreased amount Example Example ExampleExample Example Example 2 3 4 5 6 7 Ferromagnetic powder BF BF BF BF MPBF Magnetic layer thickness μm 0.10 0.10 0.10 0.10 0.10 0.10Non-magnetic layer μm 0.50 0.50 0.50 0.50 0.50 0.10 thicknessNon-magnetic support μm 4.30 4.30 4.30 4.30 4.30 4.30 thickness Backcoating layer μm 0.60 0.60 0.60 0.60 0.60 0.60 thickness Total thicknessof μm 0.60 0.60 0.60 0.60 0.60 0.20 non-magnetic layer + magnetic layerCooling zone staying 5 seconds 60 seconds 120 seconds 180 seconds 5seconds 5 seconds time Burnishing treatment Performed PerformedPerformed Performed Performed Performed before curing step Burnishingtreatment Not Not Not Not Not Not after curing step performed performedperformed performed performed performed Logarithmic decrement 0.0420.034 0.021 0.015 0.045 0.043 of magnetic layer Servo signal output %−0.70 −0.05 −0.10 −0.10 −0.90 −0.80 decreased amount

With the comparison of Comparative Examples, it was confirmed that, inthe case where the total thickness of the non-magnetic layer and themagnetic layer is equal to or smaller than 0.60 μm (Comparative Examples3 to 6), the output of the servo signal is significantly decreased,compared to the case where the total thickness of the non-magnetic layerand the magnetic layer exceeds 0.60 μm (Comparative Examples 1 and 2).

With respect to this, in the magnetic tape of Examples 1 to 7, the totalthickness of the non-magnetic layer and the magnetic layer is equal toor smaller than 0.60 μm, however, the output decrease of the servosignal was prevented, compared to that of the magnetic tape ofComparative Examples 3 to 6.

An aspect of the invention can be effective in technical fields ofmagnetic tapes for high-density recording.

EXPLANATION OF REFERENCES

-   -   1: MAGNETIC TAPE    -   10: SERVO BAND    -   11: DATA BAND    -   12: GUIDE BAND    -   SF: SERVO FRAME    -   SSF: SERVO SUB-FRAME    -   A: A BURST    -   A1 to A5: SERVO PATTERN    -   B: B BURST    -   B1 to B5: SERVO PATTERN    -   C: C BURST    -   C1 to C4: SERVO PATTERN    -   D: D BURST    -   D1 to D4: SERVO PATTERN    -   100: MEASUREMENT SAMPLE    -   101: SAMPLE STAGE    -   102: HOLDER AND TEMPERATURE SENSOR    -   103: SUBSTRATE    -   104: COLUMNAR CYLINDER EDGE    -   105: FIXING TAPE    -   106: MAGNET (FOR INDUCTION OF INITIAL VIBRATION)    -   107: PENDULUM    -   108: DISPLACEMENT SENSOR

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; a non-magnetic layer including non-magnetic powder and a binderon the non-magnetic support; and a magnetic layer includingferromagnetic powder and a binder on the non-magnetic layer, wherein thetotal thickness of the non-magnetic layer and the magnetic layer isequal to or smaller than 0.60 μm, the magnetic layer includes atiming-based servo pattern, and logarithmic decrement acquired by apendulum viscoelasticity test performed regarding the surface of themagnetic layer is equal to or smaller than 0.050.
 2. The magnetic tapeaccording to claim 1, wherein the logarithmic decrement is 0.010 to0.050.
 3. The magnetic tape according to claim 1, wherein thelogarithmic decrement is 0.010 to 0.040.
 4. The magnetic tape accordingto claim 1, wherein the total thickness of the non-magnetic layer andthe magnetic layer is 0.20 μm to 0.60 μm.
 5. The magnetic tape accordingto claim 2, wherein the total thickness of the non-magnetic layer andthe magnetic layer is 0.20 μm to 0.60 μm.
 6. The magnetic tape accordingto claim 3, wherein the total thickness of the non-magnetic layer andthe magnetic layer is 0.20 μm to 0.60 μm.
 7. A magnetic tape devicecomprising: a magnetic tape, a magnetic head; and a servo head, whereinthe magnetic tape is a magnetic tape comprising: a non-magnetic support;a non-magnetic layer including non-magnetic powder and a binder on thenon-magnetic support; and a magnetic layer including ferromagneticpowder and a binder on the non-magnetic layer, wherein the totalthickness of the non-magnetic layer and the magnetic layer is equal toor smaller than 0.60 μm, the magnetic layer includes a timing-basedservo pattern, and logarithmic decrement acquired by a pendulumviscoelasticity test performed regarding the surface of the magneticlayer is equal to or smaller than 0.050.
 8. The magnetic tape deviceaccording to claim 7, wherein the logarithmic decrement is 0.010 to0.050.
 9. The magnetic tape device according to claim 7, wherein thelogarithmic decrement is 0.010 to 0.040.
 10. The magnetic tape deviceaccording to claim 7, wherein the total thickness of the non-magneticlayer and the magnetic layer of the magnetic tape is 0.20 μm to 0.60 μm.11. The magnetic tape device according to claim 8, wherein the totalthickness of the non-magnetic layer and the magnetic layer of themagnetic tape is 0.20 μm to 0.60 μm.
 12. The magnetic tape deviceaccording to claim 9, wherein the total thickness of the non-magneticlayer and the magnetic layer of the magnetic tape is 0.20 μm to 0.60 μm.